/*
 * Copyright (c) 2025 Industrial Software Feature Database
 */
package com.comac.ins.isfd.util;

public class SnowflakeIdGenerator {
    // 起始时间戳（可设置为系统首次上线时间）
    private final static long START_TIMESTAMP = 1609459200000L; // 2021-01-01 00:00:00

    // 各部分位数
    private final static long SEQUENCE_BIT = 12;   // 序列号位数
    private final static long MACHINE_BIT = 5;     // 机器标识位数
    private final static long DATACENTER_BIT = 5;  // 数据中心位数

    // 最大值
    private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);

    // 移位
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private final long datacenterId;  // 数据中心ID
    private final long machineId;    // 机器ID
    private long sequence = 0L;      // 序列号
    private long lastTimestamp = -1L; // 上次时间戳

    public SnowflakeIdGenerator(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("Datacenter ID can't be greater than " + MAX_DATACENTER_NUM + " or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("Machine ID can't be greater than " + MAX_MACHINE_NUM + " or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    public synchronized long nextId() {
        long currentTimestamp = getCurrentTimestamp();

        if (currentTimestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards. Refusing to generate id");
        }

        if (currentTimestamp == lastTimestamp) {
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0L) {
                currentTimestamp = getNextMill();
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = currentTimestamp;

        return ((currentTimestamp - START_TIMESTAMP) << TIMESTAMP_LEFT)
            | (datacenterId << DATACENTER_LEFT)
            | (machineId << MACHINE_LEFT)
            | sequence;
    }

    private long getNextMill() {
        long mill = getCurrentTimestamp();
        while (mill <= lastTimestamp) {
            mill = getCurrentTimestamp();
        }
        return mill;
    }

    private long getCurrentTimestamp() {
        return System.currentTimeMillis();
    }

    // 解析ID
    public static String parseId(long id) {
        long timestamp = (id >> TIMESTAMP_LEFT) + START_TIMESTAMP;
        long datacenterId = (id >> DATACENTER_LEFT) & MAX_DATACENTER_NUM;
        long machineId = (id >> MACHINE_LEFT) & MAX_MACHINE_NUM;
        long sequence = id & MAX_SEQUENCE;

        return String.format("Timestamp: %d, Datacenter ID: %d, Machine ID: %d, Sequence: %d",
            timestamp, datacenterId, machineId, sequence);
    }
}
